1. Field of the Invention
The present invention relates to a combustible fuel supply system, more particularly to a combustible fuel supply system including a combustible fuel piping system capable of drawing combustible fuel out of a carburetor of the combustible fuel supply system.
2. Description of the Related Art
Referring to FIG. 1, a conventional combustible fuel supply system includes a fuel tank 1, a carburetor 21, a fuel-feeding pipe 22, and a switch 23. The fuel tank 1 is used for storing combustible fuel. The carburetor 21 is used for atomizing the combustible fuel so as to produce a mixture of combustible fuel and air, and for providing the mixture of the combustible fuel and air to an engine (not shown). The fuel tank 1 includes a tank body 11 formed with an opening 111, and a cap 13 for removably covering the opening 111. The cap 13 is formed with a vent hole 14 for fluid communication between the interior and exterior of the fuel tank 1 such that the pressure inside the fuel tank 1 is equal to the atmospheric pressure. The casing 11 defines an upper space 122 and a lower space 121 in fluid communication with each other. The lower space 121 is used for storing the combustible fuel. The upper space 122 is adapted for accommodating air when the lower space 121 stores the combustible fuel, and is in fluid communication with the vent hole 14. The carburetor 21 includes a screw bolt 211 for draining residual combustible fuel from the carburetor 21.
The fuel-feeding pipe 22 interconnects the lower space 121 of the fuel tank 1 and the carburetor 21. The switch 23 is disposed at the fuel-feeding pipe 22, and is operable to switch between a fuel-feeding state and an obstructing state so as to permit or obstruct fluid flow through the fuel-feeding pipe 22.
As shown in FIG. 1, when the switch 23 is in the fuel-feeding state, the fluid flow through the fuel-feeding pipe 22 is permitted. Moreover, by virtue of the vent hole 14, the pressure inside the fuel tank 1 is equal to the atmospheric pressure, and is not a negative pressure compared with the pressure in the carburetor 21. Further, operation of the engine causes the carburetor 21 to generate a force that causes the combustible fuel stored in the lower space 121 of the fuel tank 1 to flow into the carburetor 21 through the fuel-feeding pipe 22. Then, the carburetor 21 atomizes the combustible fuel, and the resulting mixture of the combustible fuel and air is fed into the engine subsequently. Thus, the switch 23 can be switched to the fuel-feeding state before operation of the engine. Further, when the switch 23 is in the obstructing state (not shown), the fluid flow through the fuel-feeding pipe 22 is obstructed. Therefore, the combustible fuel stored in the lower space 121 of the fuel tank 1 cannot flow into the carburetor 21 through the fuel-feeding pipe 22. Thus, the switch 23 can be switched to the obstructing state after stopping the engine.
Generally, a portion of the combustible fuel flowing into the carburetor 21 during operation of the engine remains therein. When the engine is not operated for a long time, gelatinous substance attributed to volatilization of the residual combustible fuel in the carburetor 21 can cause difficulty in starting the engine, and can even result in inability to start the engine. In order to overcome such problem, the screw bolt 211 of the carburetor 21 requires manually removal for draining the combustible fuel from the carburetor 21. However, such manual draining is inconvenient to conduct.